This invention relates to the art of wireless systems, and more particularly, to a data link protocol used to transfer information over the wireless interface.
Often wireless networks are interfaced to one or more wired networks. The various wired networks employ protocols that are unique to them and are often not appropriate for use in wireless transmission. In particular, the wireless transmission requires its own protocols to better deal with the variations and unreliability of the wireless channels. Thus, it is necessary to employ protocol translators to convert between the protocols employed by the wireless networks and the protocols employed by any wired network to which they interface. Such wireless protocols should be transparent to the wired network.
We have recognized that one good way to implement the wired to wireless network interface is, in accordance with the principles of the invention, to employ a two layered segmentation technique coupled with a two layer error detection technique. In particular, data from a source external to the wireless network, e.g., a connected wired network, typically is arranged into network layer packets, which are received at the wireless network. The wireless network then divides the network layer packets into radio data link packets, and the information within the radio data link packets is divided into portions that can be placed into, although not necessarily completely occupy, one or more time slots. Error detection is performed on each of the time slots. However, the nature of the error detection code is such that each of the time slot level transmissions may appear to be error free, and yet there is an error somewhere within the radio data link packet. Therefore, a second level of error detection is performed at the radio data link packets level to determine if there is an error within the radio data link packet. In accordance with an aspect of the invention, errors detected at the radio data link packets only require retransmission of the radio data link packets in which the error was detected, and, advantageously, do not require retransmission of the entire network layer packet as would have been required in a system that mapped directly from network layer packets to time slots.
Further advantageously, the system is able to be employed by systems that utilize dynamic constellation mapping schemes which result in different time slots for the same user being mapped with different constellations, and so they have different bit to symbol ratios. This is because such changes in the constellation mapping scheme are handled at the time slot level, and are not seen at the radio data link packet level. The segmentation of the network layer packets into radio link packets is independent of the number and size of the time slots which will carry the radio link packets. Additionally, the system is able to transmit radio link packets without requiring such radio link packets to be strictly in the same sequence that the data carried by those radio link packets appear in the network layer packet from which the radio link packets were developed. Thus, the system is robust, transparent to the wired network, and often minimizes the amount of retransmission that is required in the face of errors.